Clothing question

I'm planning to start next week and i'm a bit struggling with what clothing i'd need exactly. I realize that i should get underwear, a merino shirt and some leggins, then i have a fleece jacket and will get proper zip off hiking pants, although i'm not really sure what is exactly to get. But what goes above? When looking at the various packing lists people have posted, i'm seeing mostly rain jackets and either a down or a hardshell jacket. Is there a real difference, especially with the jackets?